For the purpose of multi-channel transmission, ribbon units containing a plurality of optical fibers have been used. A typical ribbon unit is made of a plurality of color-coated optical glass fibers which are bonded together in a matrix material. The optical glass fibers are usually coated with respective colored ink coatings, or a colorant is added to the outer primary coating, so that the individual optical glass fibers can be easily identified from each other.
Optical glass fiber ribbon units provide a modular design which simplifies the construction, installation and maintenance of optical glass fibers by eliminating the need to handle individual optical glass fibers.
When a single optical glass fiber of the ribbon unit is to be fusion connected with an optical glass fiber or with a connector, an end part of the matrix layer can be removed to separate each of the optical glass fibers. It would be advantageous to provide a mid-span access on the ribbon unit. Such a mid-span access would entail being able to easily separate the matrix layer from the optical glass fibers at a point somewhere between the ends of a length of the ribbon unit.
There have been many attempts to provide a ribbon unit in which the matrix material is easily separated from the colored coating present on optical glass fibers at any location on the ribbon unit without removal of the colored coating from the coated optical glass fibers. However, if the separation of the matrix material also removes the colored coating from the fibers, the purpose of individual fiber identification will be negated.
Published European application number 0614099A2 discloses an optical fiber ribbon unit in which the bonding between the coloring layer of the individual optical glass fibers and the matrix layer is suppressed by adding 5% by weight or less of a release agent to each of the layers. The purpose of adding the release agent is to prevent the coloring layer from being peeled off when the matrix material is separated from the optical glass fibers. Examples of such release agents include a silicone release agent or a fluorine-base release layer. While application number 0614099A2 discloses that the silicone resin or oil and the fluororesin or oil can be cured by light or heat, the disclosure in fact teaches against using such light curable release agents. Throughout that disclosure, the release agent is taught as migrating to the surface of the colored layer, and therefore the amount of release agent must be less than 5% by weight and more preferably 3 to 0.7% to prevent swelling of the resins in the layers. If the release agent was crosslinked, it would not migrate to the surface of the colored coating layer. There is no disclosure or suggestion relating to the release agent cross-linking with the monomers making up the coloring layer.
U.S. Pat. No. 4,900,126 (Jackson) discloses an optical glass fiber ribbon unit in which each of the individually coated optical glass fibers has a colored outer layer. Each of the optical glass fibers is further coated with a release agent which has a low affinity for the bonding material or the colorant material. An example of the release agent is TEFLON. The release agent creates a weak boundary layer at the interface of the colorant material and the matrix material whereby the matrix can be separated from the optical glass fibers without removing the colored layer on the individual optical glass fibers.
U.S. Pat. No. 4,953,945 discloses using a peelable cured coating layer between an outer colored layer of optical glass fibers and the matrix material whereby the matrix material can be stripped from the optical glass fibers without removing the colored layer of the optical glass fibers.
None of the above ribbon units provide an easy method for obtaining access to the individual coated optical glass fibers at a point between the ends of the ribbon unit (hereinafter "mid-span access"). The above disclosures, at best, only teach ribbon units in which the matrix material can be stripped from the optical glass fibers without removing the colored coating present on the coated optical glass fibers. Using conventional stripping methods, it is very difficult and time consuming to achieve mid-span access. Thus, there is a great need for an improved optical glass fiber ribbon unit having the ability to provide mid-span access more easily and faster than conventional optical glass fiber ribbon units. There is also a great need for an improved method to obtain mid-span access to the individual coated optical glass fibers in an optical glass fiber ribbon unit.